This relates to compression of information for electronic transmission.
Coding processes in real-time time video compression and transmission systems are done in a strictly limited period of time. For example, for high definition television 1080 p (1080×1920 60 fps), every frame is encoded during 17 milliseconds. When the next successive frame arrives at the input of compression system, it is immediately processed.
Compression is used in video and image applications such as conferencing, gaming, and entertainment.
An entropy coder is one of the key elements of video compression systems. It is also one of the most computationally complex elements. An entropy coder is a data compression block that assigns codes to symbols so as to match code lengths with the probabilities of the symbols. The problem here is to find a tradeoff between effective compression of input data and minimum complexity costs.
Usually, entropy coding is realized in modern video compression systems using paired Run-Length and Variable-Length Coding or Arithmetic coding (e.g. Tier-1 in JPEG2000). JPEG 2000 Standard Part I, Final Committee Draft vol. 0, 16 Mar. 2000. Arithmetic coding provides a better compression rate, but it is more complex. For example, Tier-1 is the most complex part of JPEG 2000, which consumes more than 50% of total computation power.